Arc-limiting shields for high frequency gaseous electric discharge switching tubes



Jan. 28, 1958 A. w. NAUGLER ARC-LIMITING SHIELDS FOR HIGH FREQUENCY GASEOUS ELECTRIC DISCHARGE SWITCHING TUBES Filed July l, 1954 INVENTOR. W N A U G L E R ALBERT BY dbz- ATTORNEY ARC-LIMITING SHIELDS FOR HIGH FREQUENCY GASEOUS ELECTRIC DISCHARGE SWITCHING TUBES Application July 1, 1954, Serial No. 440,717

2 Claims. Cl. 315-39 The present invention relates to gaseous electric discharge devices and, more particularly, to such devices employed in radar systems to provide a high intensity gaseous discharge across a discontinuity in the path of microwave electromagnetic energy'for switching the transmitted pulses to other branches of the system.

Devices of the class to be described are generally employed in a radar system to isolate either the transmitter or receiver during operation to permit the use of a common antenna. The transmit-receive or TR tube isolates the receiver during transmission of high power pulses, while the anti-transmit-receive or ATR tube functions'to decouple the transmitter when low level returning signals are received. A further device found in systems operating at very high power levels is the pre-transmit-receive or pre-TR which provides additional protection for the receiver and is mounted in wave guide structure preceding the TR tube.

The aforementioned switching devices characteristically employ a resonant window element having a central'opening or slot of multiple configurations. The central opening is enclosed with a low loss dielectric or insulating material. The dimensions of said opening are selected to present a capacitive susceptance to the electric field of the electromagnetic waves until the voltage potential at the edges of the opening builds up tothe ionizing potential of a gaseous atmosphere maintained in the tube envelope. Iionization of the gaseous atmosphere results in a high intensity gaseous discharge which destroys the resonance of the window element and causes reflection of the high power signal energy.

In the assembly of the switching devices, the resonant window element is generally hermetically sealed to a length of wave guide by soft soldering or brazing to provide a vacuum-tight enclosure. Two such elements are employed in the TR and pre-TR tubes while the ATR is provided with only one. Due to the high intensity discharge the resultant arc covers a substantial area immediately behind the resonant window element and extends to the point of seal between this element and the waveguide. Since considerable heat is dissipated during the discharge, air leaks may develop in the sealed joint, thereby destroying the vacuum condition in the tube. Transmitters available in the present day art have been increased in power output thereby enhancing the magnitude of the problem of preventing tube failures.

Further, the intense gaseous electric discharge causes sputtering of minute sealing, as well as wave guide material, particles onto the surface of the dielectric window material, thereby altering the low level electrical characteristics of the resonant element when in the non-ionized state.

Accordingly, it is an object of the present invention to provide in a high frequency gaseous discharge switch tube means for limiting the area of the discharge are positioned behind the capacitive resonant window structure.

A further object is to provide in a high frequency gaseous electric discharge switch tube means for preventing Patented Jan. 28, 1958 sputtering of metallic deposits onto the inside surfaces of the dielectric resonant window material.

A still further object is to provide in a high frequency gaseous electric discharge switch tube simple means for increasing the power handling characteristics of said tube.

Briefly, my invention contemplates eliminating the aforementioned difiiculties by providing structure in the area between the edges of the central window opening and the adjacent wave guide walls to limit the region of the high intensity electric discharge arc. The structure to be described herein comprises elongated metallic members mounted on the resonant window element in the plane extending transversely to the electric field of the electromagnetic waves.

Various embodiments of the invention will now be de scribed specifically and are illustrated in the appended drawings, in which:

Fig. 1.is a perspective view of an illustrative embodiment with a portion of the outer envelope broken away to show internal structure; I Fig. 2 is an enlarged plan view of the structure of the mvention;

Fig. 3 is an enlarged view of a component of the invention; and

Figs. 4 and 5 are perspective views of an alternative embodiment of the invention.

Referring now to the drawings, Fig. 1 illustrates a broadband transmit-receive tube. A detailed description of such devices may be found in the text Microwave Duplexers, by L. D. Smullin and C. G. Montgomery, McGraw-Hill Book Co. Inc.; New York, 1948, pages 67- 114, and only the structure concerned with the immediate disclosure will be described.

The tube shown comprises a length of rectangular hollow wave guide 1 having an input flange 2 and output flange 3 hermetically sealed at the ends thereof.

peripheral edge 6 to provide a vacuum-tight enclosure.-

The enclosure may be filled by means of tubulation 7 with a suitable ionizable atmosphere such as argon or hydrogen and a small percentage of water vapor at a reduced atmosphere of from 10 to 15 millimeters of mercury pressure.

The internal resonator structure within wave guide section 1 follows well known principles in the art and it is not necessary to the understanding of the invention to i1- lustrate such structure.

Input flange 2 is coupled to the common wave guide branch leading from the transmitter to the antenna while output fiange 3 is directly connected to the receiver of the radar system. The dimension of central opening 5, shown as a substantially rectangular slot are selected to provide for transmission of low level electromagnetic signals at a predetermined frequency. When the high power transmitter is operating, however, the voltage between edges A and B of the central opening builds up to a value in excess of the ionization potential of the selected gaseous atmosphere. An intense electric arc will then be initiated and cover essentially all of the inside surface of the resonant window element structure in flange 2. This are discharge alters the transmission characteristics of the tube and because of the position of the TR tube in the circuit all subsequent high power signal pulses will be substantially reflected to the antenna.

Increase in the power levels of present day transmitters The metallic has resulted in an extremely high temperature electric discharge which will attack the point of seal along edge 6 and cause sputtering of metal particles and air leaks.

According to the teachings of my invention; I provide a pair of elongated L-shaped metallic arc-limiting shields Shields 8 are positioned at any selected point in the region extending from the edge of opening to the outer edge of window element 4. The higher the power level the further the shields 8 may be positioned away from the opening edge. It is also possible, if desired, to have the shields contact the wave guide section 1 wallssimilar to a corner brace. The high intensity electric discharge will now be confined between shields 8, thereby protecting the point of seal 6.

The adaptability of the invention to other forms of high frequency switching devices is indicated in Figs. 4 and 5. The resonant window element structure 4 showntherein is similar to that previously described and similar reference numerals have been employed.

Fig. 4 illustrates the pre-TR switch tube comprising a shorter length of rectangular wave guide 10 without any internal resonator structure. A flange 11 and 12 with raised portion 13 and a resonant window element 4 hermetically sealed thereto encloses the ends of said wave guide 10. When mounted in wave guide structure preceding the transmit-receive tube, the walls of the wave Z guide abut against surface 14. An ionizable atmosphere is maintained within the tube by tubulation means (not shown). Either flange may be considered as the input flange and I have selected flange 12 on which to provide the arc-limiting shields 8.

In Fig. 5 an anti-transmit-receive tube is shown comprising a length of rectangular wave guide 15 closed at 16 and having one resonant window element 4 mounted at the opposite end. Flange 17 provides means for mounting the tube in suitable wave guide structure and tubulation 18 provides means for filling with a gaseous atmosphere.

The invention thus provides readily adaptable and inexpensive structure for use in electric discharge devices to protect vacuum seal joints and prevent sputtered metallic deposits from forming on the dielectric material of a resonant window.

While several embodiments have been described, it will be evident that the teachings of the invention may be applied with modifications to other gaseous electric discharge devices employing a dielectric covered discontinuity in wave guide structure across which a high intensity electric arc discharge will occur when a suflicient threshold voltage is present across said discontinuity. It is, therefore, my invention to cover in the appended claims any modifications or variations which fall within the spirit and scope of the invention.

What I claim is:

l. A high frequency gaseous electric discharge switching device comprising a gas-filled envelope of hollow pipe waveguide having a transverse metal plate hermetically sealed at an end thereof, said metal plate defining a central opening covered by a dielectric material, a pair of L-shaped metal shields mounted on opposed sides of said opening at an intermediate point between the edges of said opening and the outer edge of said plate, said shields defining wall structure extending beyond the plane of said plate in mutually parallel relationship, each shield having an overall length greater than the width of said openmg.

2. A high frequency gaseous electric discharge switching device comprising a gas-filled envelope of rectangular waveguide having a transverse metal plate hermetically sealed at an end thereof, said metal plate defining a central opening covered by a dielectric material, a pair of elongated L-shaped metal shields oppositely disposed on the interior surface of said plate at an intermediate point between the edges of said opening and the outer edge of said plate, each of said shields extending parallel to the longest dimension of said opening throughout its length and having one wall normal to the plane of said plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,872,322 Moore Aug. 16, 1932 2,391,273 Rutherford Dec. 18, 1945 2,454,741 McCarthy Nov. 23, 1948 2,478,245 Cork et al. Aug. 9, 1949 2,533,512 Samuel Dec. 12, 1950 

